The answers to your questions may be very simple, such as, Start investing with as much as you can afford to invest. If you have less amount of money then invest less amount and if you have more amount of money then invest more amount, Aim to invest consistently.
Many people invest by borrowing money from others. If one has a fixed source of income he can borrow money from others and invest but does not have to sell his investment. Because people don't always have money even if they have a job. So if he invests with a loan and later if he can repay the loan with the money he gets from his job at the end of the month, it means he can easily repay the money he borrowed from others. As a result, he no longer has to sell the investment to repay the loan.
No matter what it is not even advisable to take loan to invest in bitcoin. In bitcoin investment you must earn for you to be able to invest that is why it is an investment that one needs to have a source of income which you do not need to borrow. I think the only reason that would make one to borrow money to invest bitcoin is due to desperation, just to make money quick and when you depend in taking loan to invest bitcoin it is very possible that the investment won't last long. Loan for investment is stressful, it is better to get a source of income , no matter how small it maybe you can afford to invest with the amount you can afford and your investment will keep going smoothly.
You should not take loans for investment, no exception because investment has risks including Bitcoin, having debt also has risks and this will cause you to face two risks or problems that will frustrate you.
Although Bitcoin will guarantee you the right to profit especially in the long term you have to think about how long you are in debt and continue to pay your installments because Bitcoin does not guarantee you will get profit in a short time and this must be thought out very well because anything can happen unexpectedly which will frustrate you if it does not match your expectations.
Do not despair and do not get used to borrowing because it will not make you successful, do it according to your abilities and try or do not give up to find or get other sources of income so you can invest and that is a very good thing because it is the result of your own hard work. And besides that you do not have to immediately invest in large amounts in Bitcoin because there is a DCA strategy that can help you grow your holdings will be large in the long term if you do it routinely or periodically.